Method and apparatus for arc welding



0d. 4, 1956 D R. s. ZELLER 3,277,269

v METHOD AND APPARATUS FOR ARG WELDING rFiled Feb. 1o. 1964 a sheets-sheet 1 IN VEN TOR.

Y f FID/4,27 6.' ,2e/Zeri Oct. 4, 1966 R. s. zELLl-:R 3,277,269

` METHOD AND APPARATUS FOR ARC WELDING Filed Feb. l0, 1964 8 Sheets-Sheet 2 d BY Oct. 4, 1966 Filed Feb. l0, 1964 R.S.ZELLER METHOD AND APPARATUS FOR ARC WELDING 8 Sheets-Sheet I5 Oct. 4, 1966 Filed Feb. 10. 1964 METHOD AND APPARATUS FOR ARC WELDING 8 Sheets-Sheet 4( Oct. 4, 1966 R. s. ZELLER 3,277,269

METHOD AND APPARATUS FOR ARC WELDING Filed Feb. 10, 1964 8 Sheets-Sheet 5 rilwldly /ff F6 /wfd /ya m:

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METHOD AND APPARATUS FOR ARC WELDING 8 Sheets-Sheet 6 Oct. 4, 1966r Filed Feb. l0, 1964 INVENTOR. Fig/472:7 6.' Ze/f.

ESE- Oct. 4, 1966 R. s. ZELLER 3,277,269

METHOD AND APPARATUS FOR ARC WELDING Filed Feb. 10, 1964 8 Sheets-Sheet 7 m15 14; 4/ W42 W44 774.4

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Oct. 4, 1966 R. s. ZELLER METHOD AND APPARATUS FOR ARC WELDING 8 Sheets-Sheet B Filed Feb. l0, 1964 ,Sa urge A JNVENTOR. Fra/dfi f ZcZff,

United States Patent 3,277,269 METHOD AND APPARATUS FOR ARC WELDING Richard S. Zeller, Detroit, Mich., assiguor to Weltronic Company, Southfield, Mich., a corporation of Michigan Filed Feb. 10, 1964, Ser. No. 346,056 36 Claims. (Cl. 219-127) This application is a continuation-in-part 0f my application Serial No. 29,329, led May 16, 1960, now abandoned entitled Cont-rol Apparatus.

This inventi-on relates to control apparatus and the principles of the invention are representati'vely embodied in an arc welding apparatus w-herein a predetermined amount of `filler Wire is automatically fed into the fusion zone of the weld during each welding cycle.

An object of this invention is to improve the accuracy with which predetermined amounts of filler wire are fed into the weld puddle during arc spot welding.

Another object of the present invention is to improve the accuracy ofthe feed rate of a ller wire into the fusion zone of an arc spot Welder.

Another `object of this invention is to improve the accuracy of control over `the amount of filler wire burned.

Another object o-f the present invention is to accurately locate the initial and final positions of the tip of the filler wire in an arc spot welding operation.

Another object of this inventi-on is to improve the nozzle construction for arc welding guns to facilita-te the feeding of filler wire intoxthe Weld puddle in a manner to improve t-he weld integrity.

Ano-ther object of this invention is to establish the location of the tip of .the iller wire in an arc spot welding equipment.

Another object of this invention is to establish means for detecting the location of the tip of the filler wire in an arc spot welding equipment at a predetermined position.

Another oibject of this invention is to establish means for elect-rically isolating the liller wire from a metallic nozzle in an ar-c spot welding equipment except as a result of direct electrical engagement between the tip portion of the filler wire and the nozzle.

A further object of this invention is to insure that an arc welding operation will not be initiated until proper pressure has been established between the nozzle ofthe arc welding gun and the workpiece.

Another object of this invention is to insure that the duration of constituent operations during arc spot welding will be accurately measured. p

Another object of this invent-ion is to establish resetting of the means for timing the duration of Ithe arc and duration of subordinate functions performed during the arc welding operation as a conditioned precedent to the restriking of a prematurely Aextinguished arc.

A further object of this invent-ion is to improve the consistency of striking an arc in an arc spot welding operation.

Another object of this invention is to provide means for alternatively controlling the speed of a driving motor in accordance with the rotational speed of a tach-ometer generator or in accordance with `the armature voltage of t-he motor.

Another fea-ture of this invention is an improved means for preventing malfunctioning of the reversing mechanism associated with a reversible driving motor fro-m short circuiting the power supply for the motor.

The manner of accomplishing the foregoing objects and other objects and -features of this invention will become apparent from the following detailed description of an embodiment of the invention when read with reference to the accompanying drawings in whichz'f.

3,277,269 Patented Oct. 4, 1966 FIG. 1 is a side elevation of an arc welding gun in accordance wit-h one embodiment of the present invention;

FIG. 2 is a top plan View of the welding gun of FIG. 1;

FIG. 3 is a front View of an arc welding gun nozzle constructed in accordance with the present invention;

FIG. 4 is a side view of the nozzle of FIG. 3, partially Ibroken away for clarity;

FIG. 5 is an enlarged cross section View of a portion of the structure of F-IG. 4;

FIG. 6 is a schema-tic representation of a portion of the control circuit for the Welder;

FIG. 7 is a schematic representation of another portion of the control circuit for the Welder;

FIG. 8 is a schema-tic,representation of another portion of the con-trol circuit including a motor speed control circuit for the wire feed motor;

FIG. 9 is a schematic representation of a portion of a timer suitable for use in cooperation with the circuits of FIGS. 6-8;

FIG. 10 is a schematic representation of another portion of the timer;

FIG. 11 is a fragmentary side elevation of a modified welding gun illustrating the nozzle and a portion of the wire feed mechanism;

FIG. 12 is a diagrammatic representation of a modied arrangement for sensing the position of t-he tip of Ithe filler wire; and p FIG. 13 is a diagramma-tic representation of another modified arrangement for sensing the position of the tip of the ller Wire.

Referring to the drawings, certain of the principles'of the present invention are embodied in an arc welding gun 10 comprising a housing 12 supporting a nozzle 14 which car-ries a wire guide 90. A wire drive mechanism 16 is supported on a bracket 26 secured to and extending transversely of t-he housing 12 and includes a reversible D.C. motor M coupled to a tachometer generator TG `and to a drive roller 22 which cooperates with an idle roller 24. A suitable electrical circuit, to be described, effects control of the drive motor M to feed and retract a filler wire 28 between the drive and idle rollers 22 and 24 through a wire guide tubing 30 and guide 90 and the nozzle 14 into and from the fusion zone of the weld.

The housing 12 supports Ja slide 31 having a transversely and downwardly extending handle grip 32 and a rearwardly extending handle grip 34. The slide 31 is supported for movement forwardly and rearwardly of the housing 12 on suitable ways 35 and 36 and-is normally biased rearwardly of the housing 12 as by a pair of helical compression springs 37 ,and 38. Rearward movement of the slide 31 is limited by engagement of a depending portion 39 vthereof with an adjustment nutI 40 threadably secured toan adjustment screw 42. The adjustmentscrew 42 is disposed between the helical compression springs 37 and 38 and secured to' the housing 12. The slide 31 is movable forwardly of the housing 12 on the Vways 35 and 36 thereby compressing the springs 37 and 38.

The drive mechanism support bracket 26 extends transversely of the housing 12 for the support of both the drive mechanism 16 and a wire spool enclosure 44. A suitable filler wire spool 45, supported for rotation within the enclosure 44 by any suitable means, feeds the wire 28 between the drive and idle rollers 22 and 24.

The housing 12 supports a ller wire advance override switch 60, a manual wire feed switch 62, a manual wire retract switch 64 and a sequence initiation switch 66. A second sequence initiation switch 68 is mounted on the handle 34 and electrically connected in parallel with the initiation switch 66.

The sequence initiation switch 66, which comprises a pair of normally open contacts, is supported upon the housing 12 in a position such that the contact actuating element 70 thereof is normally in spaced alignment with a downwardly depending bracket 72 on the slide 31. In use, the nozzle 14 is placed against the workpiece, and suticient force is applied to the handles 32 and S4 to establish a rrn engagement between the nozzle and the workpiece, and to compress the springs 37 and 38 to the point at which the bracket 72, carried by the slide S1, actuates the switch 66.

In accordance with one feature of the present invention, the nozzle 14 is of tubular construction for the acceptance of a nonconsumable electr-ode 80 of, for example, tungsten, supported within a central longitudinal bore 81 of the nozzle 14 in the conventional manner. Upon the striking of an arc between the electrode 80 and a workpiece, the workpiece is heated and the metal thereof puddled. The filler wire 28 is fed into the weld puddle.

The axially rearwardly and radially outwardly extending tubular ller wire guide 90 has a lower end portion 92 secured in a complementary counterbore 94 in the nozzle 14. A bore 96 extends into the central aperture 81 of the nozzle 14 for the guidance of the ller wire 28 thereinto. The counterbore 94 has an annular arcuate seat 95 for the seating of an end portion 96 of a tubular insulating sleeve 100. The sleeve 100 is accommodated in a central bore 102 of the guide 90. An outer tubular member 104 is of insulating plastic material (for example, Tygon) and is secured to the guide 90 as by a collar 106 and has an insulating tube 108 of, for example, nylon, disposed interiorly thereof for the support of the wire 28. The inner tube 108 extends into the bore 102 of the guide 90 and biases the inner end 96 of the sleeve 100 against its seat 95 in the nozzle 14. The filler rod 28 is driven by the drive mechanism 16 through the aforementioned terminal structure into the central -cavity or bore 81 of the nozzle 14 where is is melted in the arc drawn between the electrode 80 and a workpiece.

The angular disposition of the guide 90 with respect to the nozzle 14 is such as to `feed the wire 28 into the weld puddle at the optimum angle of entry which has been determined to be approximately 20 degrees with respect to the plane of the workpiece or, if the workpiece is curved, from a tangent drawn through the arcing point on the workpiece. As is best shown in FIG. 4 of the drawings in the preferred practice, the tip of the ller wire W intersects the plane of the front or end face of the nozzle 14 substantially in line with the edge of the electrode 80.

The aforementioned construction of the nozzle 14 serves another function in accordance with a feature of the present invention in that the filler wire 28 completes an electrical circuit with the metallic nozzle 14 upon the entrance thereof into the bore 96, thereby the control the welding sequence, as will be described. Because the sleeve 100 is an insulating member, electrical continuity between the ller wire 28 and the nozzle 14 is broken upon retraction of the wire 28 upwardly into the sleeve 100. This interruption of electrical continuity between the ller wire 2S and nozzle 14l has a distinct electrical function in the con trol circuitry of the Welder, as will be described.

Suitable conduits 120, |122, and 123 are provided for the conduction of inert gases, for example, argon and helium, and .of cooling water to the nozzle y14 in the conventional manner, the flow of inert gas being facilitated by gas relief cutouts 11-8 inthe nozzle 14.

The disclosed circuits include a ymotor control circuit depicted in FIG. 8 of the drawings which controls the wire-feed motor, avcontrol circuit depicted in FIGS. 6 and 7 of the drawings which controls a number of elements of the system including the motor control circuit of FIG. 8, and a timer depicted in FIGS. 9 and 10 which controls portions of the circuit orf FIGS. 6 and 7. The circuit-s of FIGS. 6 and 7 will be described under the assum-ption that the contactor switch ZSW is in its illustrated automatic rather than manual position, in

which switch SSW is in its start position, as illustrated,

rather than in its neutral off posit-ion or in its upper continuous operation posit-ion, in which timer switch 118W is closed, in which the initial-slope switch 4SW (FIG. 7) is in its illustrated strike position 4rather th-an `in its intermediate olf position or in its lower timer position, in which the nal slope switch SSW is in its illustrated automatic position rather than in an off position and in which switch SSW is closed. It will further be assruned that the jogging switches 62 and 64 are not actuated. The operation of the circuit with any of the switches in other positions will be apparent after and from the following description.

The circuits of FIGS. 6 and 7 are energized from a source S1 upon the closure of switch 1SW, establishing an energizing voltage dilerence between conductors 250 and 252. However, no operational action occurs until switch 66 or l68 is closed. It will be recalled from the description of FIGS. 1 and 2 that switch 68 is manually actuated and that switch 66 is actuated in response to the nozzle 14 being pressed with suicient force against the workpiece.

'The closure of switch 66 or 68 connects conductor 250 to conductor `256 therefby establishing an alternating voltage between conductors 256 and 252. The closure of switch 66 or 68 also completes a circuit from conductor 250 through normally closed contacts CR6a and through the winding of relay SCR to conductor 252 as well as through normally closed contacts CR4a and through the winding of relay MCR to conductor 252. Contacts CR6a and CR4a are contacts of the spot time relay CR6 and of the wire stop delay relay CR4 in the timer 254, as illustrated in detail in FIGS. 9 and l0, respectively, of the drawings.

The operation of relay SCR (FIG. 6) results in the closure of contacts SCRb thereof which completes a circuit from conductor 250 through the closed contact of switch SSW through the normally and now-closed contacts CCRa of an arc current relay to be described, and throu-gh the winding of relay lC-R to conductor 252, thereby operating relay 1CR. The 'closure of contacts 3C-Rb also completes an energizing circuit for the welding contactor WPC.

The operation of relay ICR results lin the closure of the contacts lCRa thereof to complete a circuit from conductor 250 through normally and now-closed contacts 18CRa, through the closed contacts of switch SSW, through switch l9SW (assuming that switch to be closed) and through the winding of relay 7CR to conductor 252, thereby operating relay 7CR. The closure of contacts lCRa also completes an energizing circuit for relay 4CR to operate that relay and the resultant closure of contacts 4CRa thereof completes a circuit Ifrom conductor 256, closed contacts of switch 28W, contacts 4CRa, and through the winding of relay `SCR to conductor 252 to operate relay SCR. IRelay SCR, in operatin-g, closes its contacts SCRa to complete a latchin-g or lock-ing circuit for itself so that it will remain operated even tlhough relay 4CR later releases as long as switch 66 or 68 remains closed. It will be noted that although relay SCR, in operating, closes its contacts SCRb, the fact that relay 4CR is now openated and relay 1'8CR is now released prevents an energizing circuit from being completed for relays 6CR and 18CR at this time.

The aforesaid closure of contacts lCRa also completes a circuit through normally and now-closed contacts 18CRa, the closed contacts of switch SSW, contacts SCRa, the closed contacts of switch SSW, and through the winding of relay 10CR and unidirectional current conducting device 43RE to conductor 252 as well as through the high-frequency unit 258 to conductor 252. It will therefore be seen that as a result of the operation of relay SCR and the resultant operation of relay ICR, contactor WPC, relay 7CR, relay 10CR and the high frequency unit 258 are all energized.

The operation of the contactor WPC results in the closure of its contacts WPCa andWPCb (FIG. 7) to connect the source S2 to arc voltage source 260, and sustaining voltage derived from the source 260 is applied between the electrode 80, at a negative potential, and the work.

The closure of contacts CRa resulting from the operation of relay 10CR completes the connection of the source S2 to the arc strike voltage source 270, thereby energizing that source 270. Source 27 0 is a conventional direct voltage source adapted to rectify the alternating voltage applied thereto from the source S2, to tilter the rectified voltage, and to develop an output direct voltage between conductors 266 and 272 the latter being positive relative to the former. This voltage is of considerably higher amplitude than the voltage from source 260 and serves as an arc strike booster voltage during high frequency start. In the preferred practice, source 270 develops a direct voltage in the order of 13() to 150 volts between conductors 266 and 272. The conductor 266 is connected to the electrode 80 through the transformer secondary winding 2688 and the voltage appearing on conductor 272 is applied through the now-closed contacts 7CRb to the work.

The high-frequency unit 258 (FIG. 6) comprises a generator of high-frequency signals serving as an ionizing voltage. The frequency of these signals is not critical and in a constructed arrangement, an arc-gap discharge oscillator was employed so that the high-frequency unit developed a variety of high-frequency signals. The highfrequency unit 258 is energized, as above discussed, by the application of the voltage between conductors 250 and 252 thereto and develops the output high-frequency signal across the primary winding 268P of a transformer 268, the secondary winding 2688 (FIG. 7) of which is, as previously discussed, connected in series with the electrode 80. Since the high-frequency unit 258 and relay 10CR are operated at the same time, both the arc strike booster voltage source 270 and the radio-frequency voltage to facilitate initial ionization of the gap are concurrently applied. Conditions are thereby established for initiating an arc.

When the arc strikes so that current is flowing from the arc voltage source 260, the arc strike booster voltage source 270 and the source of high frequency ionization are deenergized. This is accomplished by associating a saturable core reactor, having a winding 276, with the lead 264. Winding 276 is connected in series with an alternating current source S3 and the winding of a relay CCR. In the absence of current through conductor 264, winding 276 offers a suficient impedance to alternating current flow to prevent energization of relay CCR. However, the flow of the arc current through the conductor 264 will produce saturation of the core associated with winding 276 to reduce the effective impedance of that winding and to permit relay CCR to operate.

When relay CCR operates, it opens its contacts CCRa (FIG. 6) to release relay ICR. Relay ICR, in releasing, opens its contacts lCRa to release relay 7CR and deenergize relay IGCR as well as to disconnect the highfrequency unit 258 from its source of energizing alternating current. In this manner, the application of the highfrequency voltage is terminated and the arc strike booster voltage source 278 (FIG. 7) is disconnected from the nozzle 14. The source 270 is deenergized shortly thereafter upon the opening of contacts lflCRa, relay 10CR being slow-to-release by virtue of the provision of the rectifier 43RE connected in series with that winding and of a capacitor 278 connected in parallel therewith.

The release of relay 1CR and the resultant opening of contacts lCRa also deenergizes relay 4CR. The resultant opening of contacts 4CRa does not change the state of relay SCR since the contacts 5CRa of that relay are closed in shunt of contacts 4CRa. The closure of contacts 4CRb, now that contacts SCRb are closed, completes energizing circuits for relays 6CR and 18CR as well as 6 an energizing circuit via conductor 280 and through the closed contacts of switch 48W for relay SCR.

Relay 18CR, in operating, closes its contacts 18CRb to complete a locking circuit for relays 6CR and 18CR in shunt of contact 4CRb. Relay 6CR, in operating, closes its contacts 6CRa which serves to initiate the timing operation of the timer 254. This timer operates in a manner to be described to control the state and change of state of a number of the contacts -in FIGS. 6 and 7 of the drawings.

It will be observed that normally closed contacts 18CRz of relay 18CR are included in the energizing circuits of relay ICR and of the high frequency unit 258. If it were not for this inclusion, mis-timing could occur. Thus, if the arc has been struck so that relay ICR is released rand relay 6CR is operated to initiate timing, if thereafter the arc becomes extinguished, and if it were possible thereafter to restrike the arc, the actual arc time would be improperly short. However, with the disclosed circuitry, once relays 6CR and 18CR have operated to initiate timing, the resultant opening of contacts 18CRa prevents re-operation of relay IOCR and of the high frequency unit 258 which would otherwise occur in response to the releasing of relay CCR (when the arcextinguishes) and the resultant reoperation of relay ICR. To restrike the arc, the operator must release whichever of the switches 66 and 68 was closed, and then reclose that switch. By this procedure, relay 6CR is released and, the timer 254 is reset and the entire cycle is reinitiated, thereby insuring that the timer is reset to zero each time that the arc is struck. y i

As was above noted, relay SCR (FIG. 7) was operated in response to the operation of relay SCR and the subsequent release of relay 4CR. Relay SCR controls the voltage source 260 and is an initial slope controlling relay. The circuits of the arc voltage source 260, including initial slope features, controlled by relay SCR, and final slope control features, controlled by relay 9CR, are conventional.

It will be recalled that in initial response to theclosure of switch 66 or 68 (FIG. 6) relay 11CR operated. yRelay IilCR, in operating, opens its contacts 11CRa (FIG. 7) to disable the forward or feed manual control switch 62 (used for jogging purposes) and closes its contacts llCRa to complete a circuit from conductor 256 through now closed Contact 16CRb, rectifier 30RE and to the winding of relay 12CR to conductor 252.v The winding of relay 12CR is shunted by capacitors 6C and 13C to render it slow-to-release for a purpose hereinafter to be noted. Relay 12CR, in operating, opens its contacts l2CRa to disable one energizing circuit for relay 14CR.

The closure of contacts llCRa also complete-s a circuit from conductor 256 through contact 16CRb and through `the winding of relay 13CR to conductor 252 as well as through rectifier S11-RE and the winding of relay 15CR lto conductor 252. As a result, both relays 13CR and 15CR are operated. These relays have contacts in the motor control circuit of FIG. 8 and serve to cause the motor M to advance the wire 28 (FIG. `2) through the guide structure 90. This advance of the filler wire 28 continues until the wire makes electrical engagement with the metal of the nozzle at the bore 96 (fFIIG. 5). When this occurs, -a circuit is completed from the voltage at the secondary winding of transformer 132 (FIG. 7), conductor 282, inductor 130, nozzle 14, wire 28, roller 22, wire 284, winding of relay 16CR, and back to the secondary winding of transformer y113512. Thus, the engagement of the wire 28 with the metallic nozzle 14 completes an energizing circuit for relay 16CR.

Relay 16OR, in operating, opens its contacts 16CRb to interrupt the energizing circuits for relays 13CR and 15CR, thereby terminating the feed or advance of the wire. The opening of contacts 16CRIJ Ialso terminates the energiza-tion of relay 12CR which, -as above noted, is slow-to-release. At the end of the release period of relay 7 12CR, contacts .12C'Ra close. While contacts `16CRa are also closed at this time, contacts CR4c are open so that no energizing circuit is completed `for the retract relay 14CR. The Wire Ichen remains in this position, just engaging the metal of nozzle 14.

The Welder remains in this condition, with the arc struck, until the occurrence of lthe first timing event produced by the timer 254. Timer 254, as Will be discussed fu-rther hereinafter, can time five separate intervals, all of which yare initiated by the closure of contact 6CRa (FIG. 6) and each of which can be set to any duration independent of the duration of `any of the lother timing intervals.

In the illustrative arrangement disclosed in FIGS. 6 and 7, five timing functions are or may -be performed: The initial slope delay, that is, the time at which relay SCR (FIG. 7) is operated to control the up-slope or initial slope period of the arc voltage source 260 (which in the illustrated setting of switch 4SW is not employed); the Wire start delay period which is the delay ybetween the initiation of timing and the time at which the Wire is advanced into the puddle; the wire stop delay period which is in the interval between energization of the timer and the time at which the wire feed is terminated by releasing relays 13CR and 15CR (FIG. 7); the -final slope delay period which is the interval between the energization of the timer and the actuation of relay 9CR (FIG. 7) to cause the .arc voltage source 260 to initiate the -fnal slope c-urrent characteristic; and the spot time period at which the Welding cycle is terminated. As will be seen, the timer |254 (FIG. 6) includes five relays designated CRZ through CR6 and for purposes of illustration, relay CRZ has been assigned the initial slope delay function (not here performed) so that its contacts CR2a (-FIG. 7) are connectable to control the energization of relay 8CR; relay CRB in the timer has beeny assigned the final slope delay function and hence its contacts CRSc (FIG. 7) control the energization of the final slope relay l9OR; relay CR4 in the timer lhas been assigned the Wire stop delay function and hence its contacts are utilized t-o control the wire feed and wire retract relays 13CR and 14CR; relay CRS in the timer has been assigned the function of controlling `the wire start delay period and hence its contacts CRtSa are also connected in energizing circuits for the Wire feed -and wire retract relays |13CR and 14CR; and relay CR6 in the timer has been assigned the over-all or spot time function and hence its contacts CR6a are connecte-d in the initiation circuit and control relays SCR and 11C-R, 4the latter of which is also controlled by contacts of the wire stop delay relay CR4.

The rst effective one of the timing events to occur, in the representative sequence, is the actuation of the wire start delay relay CRS in the timing circuit. The resultant closure of contacts CRSa (FIG. 7) completes a circuit from cond-uctor 256 through now-closed contact CR4b to complete energizing `circuits for relays 12CR, 13CR and 15CR. As will be described in c-onnection with the motor control circuits of FIG. 8, this results in an advance of the Wire into the weld puddle. I-t will be observed that the wire 28 remains in electrical engagement -with the nozzle 14 during this advance so that 'relay 16CR remains operated. The rate of advance of the wire is carefully selected and accurately controlled so that -by controlling the 'duration of the feed the amount of wire fed into the puddle can be accurately predetermined and preselected.

The Wire continues to be fed into the puddle until the wire stop delay relay CR4 in the timing circuit operates. The resultant opening of contacts CR4a (FIG. 6) releases relay MOR to open contacts 1\1CRa (FIG. 7) and close contacts `11CRb with no present effect. The resultant opening of contacts CR4b (FIG. 7) terminates the energization of relays 12CR, 13CR and 15CR. The release of relays 13CR and 15CR terminates the forward or advancing operation of the motor M to terminate the feeding of the wire into the puddle. The closure of contacts CR4c prepares an energizing circuit for relays 14OR and 15CR. However, this circuit is not complete until the slow-to-rele-ase relay 13CR has released. When this occurs and the contacts ltZORa close, a circuit is completed from conducto-r 256, contacts CRSa, contacts CR4c, contacts 12CRa, contacts 16ORa, and through the winding of relay 14CR to conductor 252 as well las through rectifier 33RE and the winding of relay 15CR to conductor 252. The opera-tion of relays 15CR and :14CR energizes the motor M to retract the Wire from the puddle. The purpose of connecting the contacts 1,2CRa in this circuit is to insure an adequate time delay du-ring which the motor can come fully to a hal-t. This is not imperative in -all circuits, of course, but is here provided since in the preferred arrangement a permanent magnet motor is employed which could become damaged if reverse currents were applied when the motor is still rotating in the forward direction.

The wire continues to be Withdrawn from the puddle until it is retracted from engagement with the nozzle 14, that is, until is drawn out of the bore 96 (FIG. 5) of the nozzle 14. When this occurs, the previously described continuity circuit is interrupted and relay 16CR releases to open its cont-acts 16CRa to release relays MCR and 15CR to terminate the retracting operation of the motor. It will be appreciated that this establishes with consistent accuracy a final position of the Wire tip which -can be effectively identical to the aforesaid accurate initial position as detected by the same tip-position sensing means. If there is a slight overrun on retract due to inertia, the wire will be advanced t-o the selected initial position preliminary to the next wire-feed operation as above described. It is feasible under some `circumstances to utilize the retracted position of the wire as the accurate initial position, that is, the act of accurately locating the initial position of the wire can be accomplished at the end of an operation, on retract, Without providing means to set or reset that position at the beginning of the next weld and wire-feed operation, although lthe illustrated arrange- -ment is preferred. Conversely, an important function of retracting the filler wire is, as above noted, to remove the Wire from the Weld area following its feed-end so as to reduce the amount of burn-off, 4after wire feed has stopped and so as to insure that Whatever burn-off does yoccur is consistent from operation to operation so that the system can be calibrated to give accurate, selectable, consistent Wire feed. From that standpoint, it is not imperative that the wire be retracted to the selected initial position or for the matter even to an accurate retracted position as long as means are provided, as disclosed, for moving the tip of the filler wire to a selected initial position prior to the next Wire-feed operation. Hence, it is not imperative that the retracted position of the filler Wire be sensed or effectively sensed .at the end of an operation, the retraction of ythe filler wire merely continuing, for example, for a period of time, as, for example, by the use of a time delay relay or the like instead of the sensing means, to terimnate `wire retraction. The amount of retraction, however, should be sufiicient to Withdraw the Wire beyond the burn-off zone, although if the wire is not retracted to the initial position sensing point, the movement of the Wire to the selected initial position, preliminary to the next subsequent weld operation, would be in a retra-cting sense. p Thereafter, in the respresentative sequence, t'he final slope delay relay CRS in the timer operates to operate the final slope relay 9CR (FIG. 7) to control Ithe final or current period. Thereafter, the spot time relay CR6 in the timer circuit operates to open its contacts CR6a (FIG. 6) to release relay SCR. Relay SCR, in releasing, opens its contacts 3CRb to release the Welding contacter WPC to terminate welding current, and produces the release of the other relays to restore the circuits to normal in prepaartion for the next cycle of operation.

The foregoing description pertains to the assumed highfrequency starting conditions.

The functioning of the equipment when the pilot arc mode of operation is utilized is identical to that above described except as expressly noted hereinafter.

In pilot arc operation, prior to the closing -of switch 66 or 68, switch 85W is operated so that each of its ganged elements is switched from its illustrated position to the opposite position land switch SSW is turned to its off position. As .a result, a circuit is completed from `conductor 250 to the upper illustrated contact of switch 8SW and through the winding of the pilot arc relay 7CR t-o 4conductor 252 to operate that relay. The closure of lthe intermediate set of contacts of switch 8SW completes an energizing circuit for relay MCR. The change of position of the lower illustrated contacts of switch SSW, coupled with the closure of the intermediate set of contacts, completes -an energizing circuit through contacts CCRa to operate relay ICR.

The operation of relay ltlCR results in the closure of contacts ltlCRa (FIG. 7) to energize the source 270 of pilot arc voltage. The operation of relay 7CR opens contacts 7CRb (FIG. 7) to disconnect output conductor 272 from the work, and the oper-ation of that relay results in the closure of contacts 7CRa to connect the output conductor 272 to the nozzle 14. This establishes a pilot arc sustaining voltage between the electrode 80 and the nozzle 14. To assist in starting the pilot arc, switch 9SW (FIG. 6) may be momentarily actuated .to complete a circuit from conductor 250, through the upper set of contacts of switch SSW, and through switch 98W to the highfrequency unit 258. As soon as the pilot arc starts, switch 98W is released.

The above noted operation of relay ICR results in the closure of contacts lCRa to complete an energizing circuit for relay 4CR. When the nozzle is placed against the work, the pilot arc transfers so as to exist between the electrode yand the Work. Due to current limiting features in the power supply 270 this is `a low-current arc of the order of, f-or example, 5 amperes. When switch 66 or 68 operates, relays SCR and 11CR operate. The operation of relay 11CR initiates the wire-feed operation to Preselect the position of the wire tip, as above described, and the operation of relay 3CR produces closure of its contacts SCRb to Vactuate the conta-ctor WPC to energize the arc voltage source 260 (FIG. 7).

. In the mean-time, the operation of switch 66 or 68 has completed a circuit through the now-closed contacts 4CRa to operate relay SCR.

When the arc voltage source 260 becomes effective to produce the full arc, relay CCR(FIG. 7) operates to open its contacts CCRa (FIG. 6) to release relay lCR which releases relay 4CR. The resultant closure of contacts 4CRb completes an energizing circuit for relays 6CR and 18CR to initiate the operation of the timer 254, .as above described.

In lthe motor control circuit of FIG. 8, the alternating voltage induced across the secondary winding of' transformer 7TA is full-wave rectified by means including rectifier 5V and is filtered by the network including capacitors 10C and 11C and resistor 20R to develop a direct voltage between conductors 154i and 152, the former of which is at a negative potential relative to the latter. This direct voltage is applied across serially interconnected resistor 21R and voltage regulating gas diodes 6V. The voltage appearing across the voltage regulator 6V is applied across a series circuit comprising variable resistor 13P, the resistive element of potentiometer 12F, and variable resistor 15P. The direct voltage appearing between the movable element of potentiometer 12P and conductor 150l is employed as a reference voltage to control the speed of the motor M in a manner to be described, and adjustable resistors 131 and 15P are utilized to adjust the maximum and minimum selectable speeds of the motor, respectively.

As noted from the prior description 0f the circuits of FIGS. 6 and 7, during either foward or reverse opyl() eration of the motor M, relay 15CR is operated, relay 17CR is released during the forward or feeding energization of motor M 'but is Operated during the retract operati-on of the motor, relay 13CR is actuated to feed the wire, and relay 14CR is actuated in lieu of relay 13CR t-o produce a retraction of the wire.

With relays 13CR and 15CR operated and relays 14CR and 17CR released to energize the motor M to feed or advance the wire, a circuit is completed from the movable element of the potentiometer 12F, contacts 15CRa, normally closed contacts 17CRa, through the tachometer generator TG, normally closed contacts 17CRb, contacts 15CRb, resistor 27R (shunted by capacitor 15C) and to the control grid of triode 7VB. The cathode of tube 7VB is connected to conductor 150 and the anode of that tube is connected through load resistor 23R to conductor 152. When the tachometer generator is geing driven as a result of the energization of the motor M to feed the wire, it will develop a direct voltage such that its left hand terminal is positive relative to its right hand terminal, so that its output direct voltage is applied Vin opposition to or buckling relation with the positive reference potential.

If tachometer generator TG is being driven too slowly, a signal deviating from the preselected value in a positive direction is applied to the control grid of tube 7VB. The resulting drop in the plate potential of tube 7VB is directly coupled to the control grid of triode 7VA through resistor 25R. The anode of vacuum tube 7VA is connected to the positive potential on conductor 152 through load resistor 22R, while the cathode of that tube is at a positive potential established at the junction of resistors 26R and 26R which are connected in series between conductors and 152. In a constructed embodiment, resistor 26K was about ten times the size of resistor 26R so that the cathode of tube '7VA was at a fairly high positive value.

The reduction of the voltage of the control grid of tube 7VA reduces the conductivity of that tube and produces an increase in the voltage at the anode thereof due to the voltage drop across load resistor 23R. This voltage is applied through resistor 29R to the control grids of dual-triode 8V, the two sections of which are connected in parallel.

Th-e `cathodes of tube 8V are connected to conductor 152 to provide, in conjunction with the positive potential applied to the grids of tube 8V from t-u-be 7VA, a negative bias. The anode circuit of tube 8V is energized from an alternating current source S3 (which may be the same source as those disclosed elsewhere in this application) via a transformer 7TB. The anodes of tube 8V are connected through rectifier 27RE to one terminal of the secondary winding of transformer 7TB and are also connected through rectifier 29RE and the primary winding of transformer 7TC to the other terminal of the secondary winding of transformer 7TB. The cathodes of tube 8V are connected to the left hand terminal of the secondary winding of transformer 7TB by means of a rectifier 26RE, and are connected to the upper terminal of the primary winding transformer 7TC via rectifier ZSRE.

Tube 8V serves in effect as a variable resistance element to control the magnitude of the alternating current in the primary winding of transformer 7TC. When the left hand terminal of the secondary winding of transformer 7TB is positive, current ows through rectifier 27RE, through both sections of dual-triode 8V, through rectifier ZSRE, and through the primary winding of transformer 7TC back to the secondary winding of transformer 7TB. When the right hand terminal of the secondary winding of transformer 7TB is positive, current flows through the primary winding of transformer 7TC, rectifier 29RE, through the paralleled sections of tube SV, rectier 26RE, and back to the secondary winding of transformer 7TB. The magnitude of this current flow will be determined by the potential at the control grid of tube 8V. Under the assumed conditions, the potential at the control grids of the sections of tube 8V will be higher than normal (in a positive sense) producing a relatively large current flow through the secondary winding of transformer 7TC.

The alternating current through t-he secondary winding of transformer 7TC is rectified Iby the full-wave bridge comprising rectifiers ZZREa, ZZREb, ZZREC, and ZZREd. The resultant positive potential appearing at conductor 156 is applied (under the assumption that relay 13CR is operated and relay 14CR is released, as above noted) through contacts 13CRa, the winding of motor M, and through contacts 14CRb and 13CRc to the negative potential appearing at the junction of rectiers ZZREC and ZZREd. With generator TG running too slowly, the potential is relatively high, the magnitude of the current flow in this path will be large and motor M will be rotated at a higher speed. This will result in an increase in the output voltage of tachometer generator TG, producing a reduction in the potential at the control grid of vacuum tube section 7VB, an increase in the current flow through section 7VA, a reduction in the voltage at the control grids of dual-triode 8V, a corresponding decrease in the conductivity of that tube, a consequent reduction in t-he current through the primary and secondary windings of transformer 7TC, and a corresponding reduction of the energizing voltage for motor M, tending to reduce its speed. In this fashion, the speed of motor M is closely regulated to a preselected value.

In the event that relay 13CR is released and relay 14CR is operated t-o produce retracting movement of the motor M, it is necessary to reverse the polarity of tachometer generator TG to produce proper operation, and this is accomplished :by operating relay 17CR in parallel with relay 14CR (as above noted) to effectively reverse the polarity of the connections to tachometer generator TG in the series circuit including the potentiometer 12F and the control grid of tu-be 7VB.

When relay 15CR is released (which, as above noted, occurs when neither relay 13CR nor relay MCR is operated) the potentiometer 12F and the tachometer generator TG are disabled to control vacuum tube 7VB over the previously discussed circuit. Under those conditions, means including potentiometer 14P are effective to establish and maintain equilibrium conditions in the control circuits in preparation for the next operation. Thus, with relays 13CR, 14CR and 15CR all released, the positive potential appearing at the wiper of potentiometer 12F is applied through contacts ISCRc, through a portion of the resistive element of potentiometer 14P and the wiper thereof, through contacts ISCRd, and through resistor 27R to the control grid of tube 7VB. The resistive element of potentiometer 14P is connected between the positive and negative terminals of the full-wave bridge rectifier including elements 22REa-22REd, so that an opposing voltage is developed across the resistive element of that potentiometer. The resultant Voltage is applied to the control Igrid of tube 7VB. If for any reason that voltage tends to be higher than that preselected by the settings of potentiometers 12P and 14P, increased current will flow through tube 8V, and an increased potential will be developed across the aforesaid full-wave bridge rectifier and applied across the resistive element of potentiometer 14P to reduce and control the magnitude of the voltage applied between the control grid and cathode of triode 7VB.

In practice, potentiometer 14P is desirably set so that the voltage applied to the con-trol grid of tube 7VB is about the same as that which will be applied to that control grid when the tachometer generator TG is being driven at the speed selected by the setting of potentiometer 12P.

It will be observed that the voltage applied across the m-otor M is also developed across the potentiometer 14P when the motor is operating. In the disclosed arrangemen-t, this voltage is not applied to the control grid of tube 7VB since contacts 15CRb are open when the motor M is running. If desired, a switch SSW may be connected in series with the winding of relay 15CR (FIG. 7) to selectively disable that relay to operate. In that case, contacts ISCRa and 15CRb will not close, so that the tachometer generator TG will not be connected to tube 7VB, and relay contacts 15CRc and ISCRd `will remain closed so that voltage developed across a portion of the potentiometer 14P will be connected in series with the voltage selected by the potentiometer 12P to the control grid of tube 7VB. Therefore, in this arrangement, the feed-back signal will be derived from the armature voltage appearing across .the motor M. It Will be seen that by selectively enabling or disabling relay 15CR, the feedback signal for regulation of the speed of the motor M may be derived either from a tachometer generator or from the armature voltage, as desired.

It will be observed that the energizing circuits for the motor M include not only normally open contacts 13CRa and 13CRb, of relay 13CR and normally open contacts MCRa and 14CRC of relay 14CR, to produce the normal reversing operation, but also include normally closed contacts 13CRb and MCRb, with the normally closed contacts 13CRb being connected in series with normally open contacts 14CRa and normally closed contacts 14CRb being connected in series with normally open contacts 13CRc and with the dynamic braking resistor SOR being connected to the junctions of those pairs of contacts. It is normally intended and expected that relays 13CR and 14CR will be energized only alternatively and in the circuits of FIG. 7 are so arranged. However, it is possible that in use, both relays would remain effectively operated at the same time either due to circuit malfunctioning, or more commonly, due to the closed contacts of one of the relays sticking or welding. This condition, of course, would produce a short circuiting of the power supply including the rectiiiers 22REa through ZZREd. To avoid this malfunctioning, it is customary to provide mechanically interlocked relays so that neither can .operate unless the other is released. By virtue of the provision of the additional two sets of normally closed contacts 13CRb and 14CRb, -the additional lexpense of providing mechanically interlocked relays is obviated. Thus, for example, if relay contacts 14CRa and 14CRC remain closed after the actual (due to contact welding) or ostensible (due to circuit malfunctioning) de-energization of relay 14CR, and if relay ISCR is thereafter operated to close contacts 13CRa and 13CRc, the power supply cannot be shorted through contacts 13CRa and 14CRa since contacts 13CRb are now open, and the power supply cannot be shorted through contacts 14CRc and 13CRc since contacts 14CRb are now open.

The program timer of FIGS. 9 and 10 comprises a driving amplifier V4, a plurality of timing amplifiers V5, V12A, and V12B, a plurality of counter tubes V1, V2 and V3, and a plurality of coincidence circuits including thyratrons V6, V7, V8, V9 and V10. In these circuits, a source of direct voltage is represented as a circle and it is to be understood that the other terminal of each such illustrated source is connected to ground.

The counters V1, V2 and V3 are representatively illustrated to be cold cathode glow transfer or stepping tubes which may, for example, be of the type manufactured by Ericson Telephone Ltd., of Great Bri-tain, type GSlOC. These tubes are commercially available in the United States of America. In general, each of these stepping tubes, such as stepping tube V1, comprises a plurality of cathodes designated l-10, inclusive, an anode 200 common to all those cathodes, and a first and second plurality of intermediate, transfer or guide electrodes interposed the main cathodes Nos. l-l0. Since the electrodes in each of these groups of intermediate electrodes are electrically interconnected, the two groups of electrodes are,

13 for convenience of illustration, designated as single electrodes 211 and 212.

The anode 200 is connected through resistor R15 to a source of positive direct potential on conductor 215, the main cathodes Nos. l-9 are connected to ground through individual load resistors R29-R37, and main cathode No. 10 is connected to zero line 217 through resistor R33. The tube is designed so that with the properly selected value of resistor R15, discharge can be supported, at any one time, between the anode and but one of the main cathodes Nos. 1-10 so that the tube will commutate. The discharge path is advanced so that it exists between the anode and the successive cathodes by applying suitable pulses to the transfer or guide electrodes 211 and 212, the direction of advance being selected by the sequence of pulsing of those two groups of electrodes.

In the disclosed arrangement, the tube is initially set so that conduction exists between anode 200 and main cathode No. 10, and the discharge path is advanced from cathode to cathode in numerical order, the discharge first transferring from cathode No. 10 to cathode No. 1, thence to cathode No. 2 and so forth. This is accomplished by applying a pulse to transfer electrodes 212 slightly in advance of the application of a pulse to transfer electrodes 211. It will be appreciated that other forms of counting devices may be employed, that other forms of cold cathode gaseous discharge counting tubes may be employed, and ythat if the direction of discharge advance is established inherently in the tube by the construction and configuration of the cathodes or otherwise, the necessity for providing two time-phased input pulses can be avoided.

As will be seen, the function of tube V1 and of the other counter tubes disclosed, is to count a plurality of serially received input pulses and to transmit output signals whenever selected numbers of those pulses have been received. The sixty-cycle alternating line source is utilized as a pulse source inthe present Vsystem so that the counters in effect count cycles of the sixty-cycle line frequency. 4

Prior to the closure of switch SW11, relay CR1 is released and its contacts CR1c are open. Consequently, a potential of approximately 150 volts negative (relative to ground) is applied to the zero line 217. As a result, the No. l cathodes of the counter tubes V71, V2 and V3 arereturnedto a source of quite negative potential relative to the ground potential to which the other lcathodes of those tubes are returned. This selective application of a high negative potential to the No. lOvcathodes, in `conjunction with the application of the high negative potential to the other elements connected to the zero line (as will become apparent from the ensuing description) results in each of the counter tubes being initially set to a condition in which the conduction exists between the anode and the No. 10 cathode thereof.

When line switch SW11 is closed, the source of alternating potential S5 is connected across the primary windings of transformers T1 and T2, with no present operational effect. However, when the initiating switch or contacts GCRd are closed, the energizing circuit for relay CR1 is completed and that relay operates. Relay CR1, upon operating, closes its contacts CRla to connect a positive direct voltage to conductor 216 over which it is supplied through load resistor R7 to the anode of thyratron V4, through resistor R65 and the winding of relay CR2 to the anode of thyratron V6, through resistor R70 and the winding of relay CRS to the anode of thyratron V7, through resistor R5 and the Winding of relay CR4 to the anode of thyratron V8, through resistor R80 and the winding of relay CRB to the anode of thyratron V9,Kthrough resistor R85 Vand the winding of relay CR6 to the Ianode of thyratron V10, and across a voltage divider circuit to be described. Relay CR1, in operating, also closes its contacts CRlc to connect the zero line to ground to relieve the normalizing signal and enable the circuit to operate.

When the circuit is in operation, pulses derived from the alternating voltage supply are applied to the transfer electrodes of the counter tube V1 by means including tube V5. Tube V5 is a pentode the cathode and suppressor grid of which are grounded, the anode of which is connected through plate resistor R11 to a positive direct voltage on conductor 214 and the screen grid of which is connected through the secondary winding of transformer T2 in series with resistor R3 to a .source of negative potential indica-ted on the drawings to have a magnitude of a negative 100 volts. Transformer T2 is preferably a peaker type transformer in which the core has an air gap so that there will be no effective breakdown of fiux thereacross un-til the voltage appearing across the primary winding reaches a preselected value. This feature, coupled with the application of a large negative biasing voltage through resistor R3, results in the application of a positive pulse of energy to the screen grid of vacuum tube V5 at, or approximately at, the 90 point on the positive half-cycle of the alternating voltage wave form appearing across the primary winding of transformer T2. However, for reasons that will become apparent hereinafter, it is desirable that no such pulses be applied to the screen grid of tube V5 unless the coincidence circuit including thyratron V10 is nonconductive. Therefore, the screen grid of tube V5 is connected through resistor R8 to the anode of thyratron V10. If thyratron V10 is conductive, its anode potential is lower than the potential on conductor 216 due to the drop across resistor R and the winding of relay CR6, and the algebraic sum of the negative one hundred volt poten-tial applied through resistor R3, of the relatively lowv positive potential applied through resistor R8, and of the positive pulse developed across the secondary winding of transformer T2 is not sufficient to cause vacuum tube V5 to produce the requisite output signal, even if other conditions are met. However, if thyratron V10 is extinguished, the positive potential at its anode is substantially equal to the positive potential on conductor 216 and the resultant voltage is applied through resistor R8 to the screen grid of vacuum tube V5 and is such that the algebraic sum of the voltages applied to that screen grid at the positive peak of the voltage developed across transformer T2 is sufiicient to actuate tube V5. Thus, non-conductivity of thyratron V10 is a condition precedent to the effective operation of vacuum tube V5.

The circuits connected to the control grid of tube V5 also establish another condition precedent to its effective operation. Thus, that control grid is connected to a 'source of negative potential (representatively negative 20 Y volts) through the resistance network comprising resistors R9 and R10, and is connected to ground through the cathode resistor R6 of thyratron V4 and uni-directional current conducting device RE19. When thyratron V4 is non-conductive, therefore, a negative bias is applied between the control grid and cathode of vacuum tube V5 to prevent the effective production of output signals by that tube,

Thyratron V4 is initially disabled because its plate circuitis open at contact CRla of relay CR1. When relay CR1 operates, closing contacts CRla, the output circuit of thyratron V4 is energized, but thyratron V4 will not immediately fire due to a provision of a short time delay to ensure that relay CR1 has operated and that any chattering of its contacts have dissipated to prevent any improper operation of vacuum tube V5. Thus, the alternating voltage applied across the primary winding of transformer T1 upon the closure of switch SW11 will induce an alternating voltage across the secondary windingV of that transformer which is applied across serially interconnected resistors R1 and R2. The voltage across resistor R1 is half-wave rectified by means including rectifier RE1, which is connected in series with normally-closed contacts CR1b of relay CR1. This rectified voltage is filtered by and developed across resistor R4 in parallel with capacitor C1, and the polarization of rectifier REll is such that 15 the right hand terminal of resistor R4 will be negative relative to the left hand terminal thereof. The alternating voltage appearing across resistor R2 is applied in series with the negative direct voltage appearing across resistor R4 to the control grid of thyratron V4 through current limiting resistor R5. The magnitude of the direct voltage across resistor R4 is suicient to prevent tube V4 from firing even with plate voltage applied. When relay CR1 operates to open contacts CRlb, the rectifying circuit including rectifier REI is disabled, but a hold-off voltage will continue to be applied to the control grid of thyratron V4 until capacitor C1 is adequately discharged through resistor R4. When the charge on capacitor C1 is dissipated to a preselected value, thyratron V4 Will be fired as the alternating voltage across resistor R2 increases in a positive direction. In the preferred arrangement, transformers T1 and T2 are so connected that the voltage at the upper end of the'secondary winding of transformer T2 is 180 out -of phase with voltage at the upper end of the secondary winding of transformer T1. Thus thyratron V4 will be fired during a half cycle of the supply during which no positive pulse is being applied to the screen grid of tube V5. In this fashion, thyratron V4 is fired approximately 180 before the next positive pulse will be applied to the screen grid of tube V5.

When thyratron V4 fires, the potential at its cathode rises due to the potential drop across resistor R6, correspondingly raising the potential at the junction of resistors R9 and R10 and thereby applying a voltage to the tube V5 which will enable that tube to operate in response to the positive pulses applied to its screen grid.

After the foregoing conditions precedent to the effective operation of vacuum tube V5 are met, a negativegoing pulse will appear at the anode of tube V5 at each positive pulse supplied to the screen grid thereof. These negative-going pulses are applied through capacitor C4 and through serially interconnected resistors R12 and R14 to a source of relatively low positive potential. Since transfer cathodes 212 are connected at the junction of resistors R12 and R14, their potential will be sharply re duced at each such pulse, producing a transfer of the discharge within the counter tube V1 so that it exists between the anode 200 and the transfer electrode 212 which is adjacent the last conducting cathode, in the initial condition, cathode No. 10.

Each of the series of negative-going pulses at the anode of tube V5 is further applied through capacitor C4, resistor R13, and capacitor C6 to ground, with the transfer electrodes 211 being connected to the junction of resistor R13 and capacitor C6. The time constant of the network including elements R13 and C6 is selected so that the application of a negative-going pulse to the transfer electrodes 211 will be delayed for an appropriate interval relative to the time that the pulses are applied to the transfer electrodes 212. At each such application, the discharge path in tube V1 is transferred so that it exists between the anode 200 and the next adjacent transfer electrode 211 and, upon the termination of the negative pulse to transfer electrodes 211, conduction is established between anode 200 and the next succeeding main cathode, following initial condition, cathode No. 1. Successive pulsing of transfer electrodes 212 and 211 will cause the conductive path to advance along the series of main cathodes.

At the tenth input pulse, the conductive path will be transferred so that it exists between the anode 200 and the No, 10 cathode of units counting tube V1. The resultant sudden increase in the potential at that cathode results in the application of a positive pulse to the control grid of vacuum tube V12A via the network comprising capacitor C8 and resistor R17. In response thereto, vacuum tube V12A will apply a negative pulse to transfer `electrodes 222 of the tens counter V2 by means of the network including capacitor C9 and resistors R19 and R21 and will, a short delay thereafter, apply a negativegoina pulse t0 the transfer electrodes 221 of the counter tube V2 by means including capacitors C9 and C11 and resistor R20. In response to these time-spaced pulses applied to transfer electrodes 222 and 221 of the tens counter tube V2, the conductive path therein will be transferred so that it exists between the anode and the No. 1 cathode thereof.

The next succeeding or eleventh input pulse will cause the conductive path in the units counter tube V1 to again step to the No. 1 cathode of that tube and succeeding pulses will cause the units tube V1 cyclically'to count. Each time that the conductive path in the tube includes the No. l0 cathode of that tube, an output or carry pulse will be transmitted to advance the conductive path in the tens counter tube V2 one step.

At the hundredth input pulse, the conductive path in the tens tube V2 will be advanced to exist between the anode and the No. 10 cathode thereof, which will cause a positive pulse to be applied to the control grid of tube V12b which will result in the application of a counting signal to the hundreds counter tube V3 in a manner similar to that above described. In this fashion, onethousand input pulses can be counted by providing units, tens and hundreds counter tubes cascaded as illustrated.

Each of the cathodes of the units counter tube V1 is connected to each corresponding stationary contact of each of a plurality of selector switches SW1, SW4, SW7, SW10 and SW13, each of the main cathodes of the tens counter tube V2 is connected to a corresponding one of the stationary contacts of a plurality of selector switches SW2, SWS, SWS, SW11 and SW14, and each of the main cathodes of the hundreds tube V3 is correspondingly connected to each corresponding stationary contact of each of a plurality of selector switches SW3, SW6, SW9, SW12 and SW15.

The concidence circuits including thyratrons V6-V10 serve to detect the concurrence of conductivity at each of three selected main cathodes of the three counter tubes V1, V2 and V3. Thus, each of the thyratrons V6-V10 will be fired at an individually preselectable count. Each of these coincidence circuits, such as the coincidence circuit including thyratron V6, includes three unidirectional current conducting devices such as diodes RE4, RES and RE6 which may be characterized as the units, tens, and hundreds diodes in that they are connected through the stepping switches to selected cathodes of the units, tens and hundreds counter tubes V1, V2 and V3. Diode RE4 is connected to the wiper of selector switch SW1 which, in the illustrated setting, is connected to the No. 4 stationary contact of that selector switch and hence is connected to the No. 4 cathode of counter tube V1. Diode RES is connected to the wiper of selector switch SW2, which in the illustrated setting is connected to the No. 3 contact of that switch and hence to the No. 3 cath-ode of the tens counter tube V2, .and diode RE6 is connected to the wiper of switch SW3 which is shown to be positioned in association with the No. 2 contact thereof and hence is connected to the No. 2 main cathode of tube V3. As a result, in the illustrated settings, thyratr-on V6 is arranged to be fired at the two-hundred and thirty-forth input pulse. The setting, of course, is purely arbitrary and may be varied as desired in accordance with the timing functions sought to be performed.

Similarly, the diodes RE7, RES and RE9 are associated with selector switches SW4, SWS and SW6 so that thyratron V7 will be fired, as a representative example, at a different preselected total count of the input pulses. Thyratrons V8, V9 and V10 are also elements of coincidence circuits including individual diodes connected to india/idual selector switch banks in a corresponding fashion.

Since relay CRI is operated, a circuit is completed from a source of positive 200 Volt potential, through contacts CRla, conductor 216, resistor R59, and resistor R60, to ground through contacts CRlc. As a result, a positive potential appears at conductors 224. At any time that RE6 under'this circumstance is quite low. This relatively low positive potential is applied in series with a negative 2O volt potential across voltage dividing resistors R97 and R62 and the resultant voltage appearing at 'the junction" of resistors R97 and R62 Vis Vapplied through current limit-l ing resistor`R63 to the control grid'of ,thyratronf V6. -The` magnitude of this potential is insufficient to rethyraton V6, andthe parameters ofthe circuits are selected so that the potential applied to the control grid of thyrat-ron V6 will not be adequate to permit that thyratron to fire as long las the cathode to which any one of .the rectifiers` RE4-jRE6 is connected is not an element of the conductive path in the associated countertube. Therefore, inthe illustrated arrangement, "atbutI only at thepreselected count, all three of the counter-,tube cathodes to which the diodes lRE4-RE6 are then selectively connected Aare supporting conduction and are at a potential which is` positive relative to ground. As a result, rectiters `RE4- RE6 will present `an appreciablyhigher impedance to thevow of current from conductor 224 through resistor v R61 via the previously traced "circuits. The voltage 'drop across resistor R61 will accordingly fall and the potential applied to the controlugrid of thyratrony V6'will correspondingly rise to a value sufficient to tire that thyratron. When thyratron V6res, .relay CRZ included v,inf its .pl-ate,

circuit, will be energized and will remain energized until` relay CRI `isl released. l l i In a similar )ma er,'thyratron' V7 will be tired at a preselected count to operate relay v(2K3, thyratron V8'wi11 actuated at a preselected count to operate relayCRkt, thyratron V9 will be actuated at a preselected countto.

operaterelay CR5,r`and thyratron V10 willbe actuated ata preselected count to energize relay .,CR6. a I

1 The sharp reductionY in' plate potential' of thyratron Vlresulting from the conductivity thereof, is applied tov resistor R8 to terr'ninate the operation 'of vacuumtube V5.'

This terminates operation of the counting circuit.` Therefore,'wlnle the contacts of Vrelays CK2-C116 may be connected in Vany fashion to perform lany desired function and while there is no ItqCCSaIY order in which those' relays become operated, resistor R8 should be connected tot-he anode of the last one" `ofthe employedz'thyratrons which is" to be tired. With the illustrated 'vconnectiomjit is assumed thatrelay CR6is7 to operate `at the highest count. M Y y In the` arrangement illustrated' in FIGS.' 1-5 of the. drawings, `thesensing ofthe'position of thetip of the lfiller a tube-319, anda hollow guide liner v320 carrying the feed` wire 322, is secured to the rear of assembly 312. The wire 322 is driven by a motor assembly (such as the assembly illustrated in FIGS. 1-5) through liner 320, through an insulating sleeve 324 disposed within assembly 312, and through a metallic wire feed nozzle 326 threadedlyconnected to the end of assembly 312. Nozzle 326 directs the wire 322 through aperture 304. The assembly` 312, and hence the nozzle `326, maybe locked in selected angular position by means of an adjusting nut 330 which is threaded on the rear end of assembly 312 and which forces a pointer assembly 331 into abutment with a surface of bracket 306. Bracket 306 is desirably also ad-` justable longitudinally of the gun so that the angle of feed of the wire may be adjusted. While yet permitting the feed wire to be directed so that it will intersect the` plane of the face of the nozzle about in alignment withv the near edge vof the electrode 301, as illustrated. In a constructed arrangement, the angle of feed was adjustable from an angle of 10 from the plane of the face of nozzle 302, as illustrated, to about 35, as indicated by axis 332.

While the aperture 304 can be designed so that the tip of the filler wire 322 contacts nozzle 302 and permits electrical `sensing of the location of the tip of the filler wire in a manne-r similar to that described in connection with FIGS. 1-5, in the illustrated arrangement the pre- Wire is Iaccomplished electrically.V In the embodiment of FIG. ll, this sensing isy also accomplished electrically, by' detecting the point'of engagement of the iller"wire"withv a filler wire nozzle=326 `which is positioned in apre` selectable relationship to nozzle 14.V 4 u e i In the arrangementillustrated'in FIG. 1l of the drawings, the fr-agmentarily` illustratedy arc spot gun 300 .isY provided `with an electrode `301 'disposed within a hollow nozzle 302`engageabrle with the workpiece and havingone or more apertures, `suc'h as aperture 304, vin the side wall thereof.- In this fcase, the aperture is an enlarged slot extending to the forward face? of the nozzle 302, as distinguished from the arrangement of FIGS. 145 inwhich the aperture' is ahole inthe side wall of the nozzle. TheV term aperture isj intended to` belgeneric.v A support bracket 306 is slidably connected to' the gun `300 as by means of a* screw 308 and slide 3105A wire guide assembly 312` is pivotally connected to bracket 306 by means of a pair of trunnionsincluding trunnion 314. A wire feed tube assembly 316, comprisinga casin'g'318,

selectedposition of the tip of the filler wire 322 is, as illustrated, at the point of its electrical engagement with wire feed nozzle 326, that is, just as it leaves sleeve 324 and contacts nozzle 326. The position sensing circuit,

' in this arrangement, includes the Wire 322, nozzle 326,

bracket 306, and the gun 300, and controls the energization of relay 16CR (FIG. 7), for example.

`This embodiment, as the irst `described embodiment,

permits accurate control orf the amount of liller Wire introduced into the weld puddle. selected position of the tip of the filler wire may also be. sensed mechanically, as by a limit-switch arm 340 (FIG...12) engageable with and movable by the tip of the v filler, Wire 322 at a selected position, as schematically illustrated in FIG. 12, pneumatically, as by employing a sensing apparatus 342 to sense when the flow of air, or better, argon, from a source 344 and through transversely aligned apertures 3'46-348 (FIG. 13) in the tube 90', for example, is interrupted or permitted by the Wire 322 as schematically illustrated in FIG. 13, or otherwise. In any such case, the sensing means may control relay 16CR (FIG. 7). v

While it will be apparent that the embodiments of the inventionherein disclosed are well calculated to fulfill the objects of the invention, will be appreciated that the invention is susceptible modilication, variation and change without departing from the proper scope or fair meaning ofthe subjoined claims.

-What is claimed is:

y1. In an ar-c welding apparatus in which filler wire is suppliedto the weld puddle, a hollow electrically conductive nozzle, a nonconsumable electrode within said nozzle, an aperture in the side wall of said nozzle o-f substantially the same diameter a's the filler wire having a portion electrically engageable with the filler Wire and a portion for supporting the wire` in insulating relation to the nozzle,

motor control means responsive to electrical engagement and disengagement of said filler wire with the electrically conductive portion of said nozzle, and motor means controlled by said motor control means for .drivingthe filler wire through said aperture.

2. The combination of claim 1 in which said aperture is inclined at Ian .angle of approximately 20 degrees to the plane of the face of the nozzle.

3. The combination of claim 1 further including means for electrically insulating the filler wire from saidnozzle except solely as a result of direct electrical enegagement between the iiller wire and the walls of said aperture.

4. They combination of claim 3l further including a It is contemplated that theguide member secured to said nozzle and having a longitudinalbore aligned with said aperture, and an insulating member disposed within fthe bore in said guide member and having a longitudinal bore aligned with said aperture in said nozzle and having a diameter substantially equal to the diameter ofthe filler wire. y

5. The combination of claim 4 in which said liller wire makes electrical engagement with the walls of said aperture in said nozzle when the wire is advanced to project from said insulating member into said aperture in said nozzle.

6. The combination of claim 3 further including detecting means for detecting electrical engagement between the filler wire and the walls of said aperture in said nozzle. 7. In an arc welding apparatus, a hollow metallic nozzle, a consumable metallic member movable relative to said nozzle member and engageable therewith in the course of its travel, means for insulating said consumable member from said nozzle member except upon engagement therebetween, means for advancingsaid consumable member relative to said nozzle member, and means responsive to electrical engagement between said consumable member and said nozzle member for controlling said advancing means.

8. The method of accurately controlling the amount of filler wire introduced into a weld puddle during an arc spot welding operation which comprises the steps of electrically sensing an accurate initial position of the tip of the ller wire, advancing the ller wire into the weld puddle iat a controlled rate for a preselected period of time, and retracting said ller wire at the end of that time.

' 9. In an arc welding apparatus in which ller Wire is supplied to the Weld puddle, a hollow nozzle, a nonconsumable electrode within said nozzle, an aperture in the side wall of said nozzle of substantially the same diameter as the filler wire, a driving motor rotatable at a speed determined by the magnitude of the voltage applied thereacross for advancing and retracting said filler wire, means for detecting the voltage applied across said motor, a tachometer generator coupled to and driven by said motor, a sou-ree of reference voltage, a source of energizing voltage for said motor, control means for controlling the magnitude of the voltage applied across said motor from said source of energizing voltage, selectively manually operable switch means having two positions, means controlled by said switch means and eiective when said switch means is in one of said positions for controlling said control means in accordance with the combination of said reference voltage and the output voltage of said tachometer generator, means controlled by said switch means and effective in the other position of said switch means for controlling said control means in accordance with the combination of said reference voltage and the voltage appearing across said motor `and means including said motor for driving the `filler wire through said aperture.

10. In an arc welding apparatus in which filler wire is supplied to the weld puddle, a hollow nozzle, a nonconsumable electrode within said nozzle, guide means including electrical insulating means for guiding the said wire adjacent said nozzle and for electrically insulating the wire from said nozzle, drive means for driving the wire through said guide means and into electrical engagement with said nozzle, and means responsive to the electrical engagement of the wire with said nozzle for controlling said drive means.

11. The combination of claim in which said guide means supports the wire at an angle with respect to `thel axis of the nozzle in which the tip of the wire intersects the plane of the face of the nozzle substantially in line with the edge of said electrode.

12. In an arc welding apparatus, a nozzle engageable with a workpiece and having an aperture in a side wall thereof, means for supplying ller wire through the aperture in said nozzle at a preselected rate, a noncon- 20 sumable electrode within said nozzle, means for striking an arc between said electrode and the workpiece, timing means Vfor controlling the time during which Athe filler wire is advanced through the Aaperture in the nozzle, means eiective in response to the initiation of the arc to initiate the operation of said timing means, and means responsive Yto the extinction of said arc to establish resetting of said timing means as a condition precedent to. the reinitiation of the arc. v

13. In an arc welding apparatus for welding a workpiece, a metallic nozzle engageable with the workpiece,` an electrode within said nozzle, working voltage means for establishing a working direct voltage between said electrode and the workpiece, booster voltage means for establishing a direct voltage between said electrode andthe workpiece which is highv in magnitude relative to said working voltage, ionizing means for establishing a highfrequency ionizing voltage difference between said electrode and the workpiece, control means for causing s aid booster voltage and said ionizing voltage to be concurrently applied between said electrode and the workpiece, and control means effective while said working voltage means is operating for terminating the operation of said ionizing means and eiective' a preselected delay interval thereafter to terminate the operation of said booster voltage means.

14. In an arc welding apparatus for welding a workpiece, a metallic nozzle engageable with the workpiece, an electrode within said nozzle, working voltage means for establishing a working direct voltage between said electrode and the workpiece, booster voltage means for establishing a direct voltage between said electrode and the workpiece which is high in magnitude relative to said working voltage, ionizing means for establishing a high-frequency ionizing voltage diierence between said electrode and the workpiece, control means for caus-` ing said -booster voltage and said ionizing voltage to be concurrently applied between said electrode and the workpiece, and control means effective while said working voltage means is operating for terminating the operation of said ionizing means and eifective a preselected delay interval thereafter to terminate the operation of said booster voltage means, said control means being effective in response to the establishment of-an arc between said electrode and the workpiece and in response to the tlow of current from said working voltage means through the arc.

. 15. In an arc welding apparatus for welding a workpiece, a metallic nozzle engageable with the workpiece, an electrode within said nozzle, working voltage means for establishing a working direct voltage between said electrode and the workpiece, voltage supply means having two `output terminals for producing a voltagewhjch is high in magnitude relative to said working voltage means for connecting one of said terminals to said electrode and manually actuatable means for alternatively connecting the other terminal of .said voltage source means to-said nozzle and to the work-piece, and ionizing means effective under the control of said manually actuatable means alternatively to apply a high-frequency ionizing voltage difference between said electrode and said nozzle and between said electrode and the workpiece.

v16. In an arc welding apparatus in which filler wire is supplied to the weld puddle, a lillerA wire, a hollow electrically conductive nozzle, a nonconsumable electrode within said nozzle,-an aperture in the sidewall of said nozzle of substantially the same diameter as the filler wire having a portion electrically engageable with the iller wire, means for electrically insulating the ller wire lfrom said nozzle-except solely as a result 'of direct electrical engagement between the filler wire and the walls of ysaidaperture, rdetecting means for detecting electrical engagement -between vthe filler Wire`and the walls of said aperture in said nozzle, control means retions which comprises Ythe steps of establishing engagemeut between the nozzle and the workpiece, advancing the filler wire relative to the nozzle from an accurate initial `position spaced from the weld puddle into the weld puddle at a controlled rate for a preselected period of time,'and after `said period of time removing said filler wire relative to the nozzle to move the tip of the filler wire to said accurate initial position, at least a portion of said movement being in a retracting sense to move the tip of the filler wire out of andaway from the weld puddle to control burn off and ocurring while the nozzle is in engagement with the workpiece.

18. The method of claim 17l further including the step of establishing an arc between an electrode and a workpiece to form the'weld puddle, and in which said advancing of the filler wire and said portion of said movement of the filler wire lboth occur prior to the termination of the a'rc.

19. The method of claim 17 in which said movement in a retracting direction terminates while the nozzle remains in engagement with" the workpiece and when the tip of the filler wire reaches said initial position.

20. The method of claim 17 in which portion of said movement in a retracting direction occurs while said nozzle remains in engagement with -a workpiece during one weld operation, and in which said movement of said filler wire includes further movement to said accurate initial position.

` 21. The method of claim 20 in which further said movement 'is in an advancing Vsense and occurs while said nozzle is inengagement with a workpiece preliminary to the next weld operation.

- 22. In an arcwelding apparatus in which a weld puddle is formed on a workpiece as a result of an arc established between an electrode and the workpiece and .in which filler wire is supplied to the weld puddle, a hollow metallic nozzle engageable with a workpiece and having an aperturel through a side wall thereof and surrounding an end portion of the electrode, means for advancing the filler wire into preselected relationship with said nozzle, means effective thereafter for advancing a preselected amount of the filler wire through the aperture in said nozzle to positively control the amount of filler wire added to the Weld puddle, and 'means effective when said preselected amount of filler wire has been advanced for retracting the remaining filler wire to preclude additional burn-off of said wire.

23. In an arc Welding apparatus, a nozzle engageable with a workpiece and having an aperture in a side wall thereof, feed means effective when actuated for supplying filler wire through the aperture in said nozzle at a preselected rate, a nonconsumable electrode Within said nozzle, means for striking an arc between said electrode and the workpiece, timing means effective a settable time after actuation for actuating said feed means, sensing means for sensing the initiation of the arc, and means controlled by said sensing means and effective in response to the initiation of the arc to actuate said timing means.

24. The combination of claim 23 further including second timing means for controlling the time at which the advance of said filler wire is terminated and means effective at the termination of said time and while the arc continues for retracting the filler wire.

25. In a motor control system, a reversible direct current motor rotatable in a direction determined by the polarity of the voltage applied thereto and having two 22- terminals, a source of direct voltage having two terminals, first and second normally alternatively actuable switch means, said first switch means having first normally open and second normally closed and third normally open contacts the states of which are normally concurrently changed, said second separately operable switch means having first normally open and second normally closed and third normally open contacts the states of which are normally concurrently changed, means comprising said first and third contactsof said first switch means' and saidV second contacts of said second switch means for connecting at one time one terminal of said lsou-ree to one terminal of said motor and for connecting the other terminal ofsaidsource` to the other terminal of said motor for driving said motor in one direction, said second contacts of said second switch -means and said thirdcontacts of said first switch means being connected in series withk one another Ibetween one terminal at the motor and one terminal of the source, and means comprising said `first and third contacts of said second switch means and said second contacts of said first switch means for connecting at one time said one terminal of said source to said other terminal of said motor and for connecting said other terminal of said source to said one terminal of said motor for driving said motor in the. opposite direction, said second contacts of said first switch means and said third contacts of said second switch means being connected inseries wit-h one another between one terminal of the motor and one terminal of the source.

26. In an arc weldingapparatus in which filler wire is supplied to the weld puddle, a hollow nozzle, a nonconsumable elect-rode within said nozzle, an. aperture in' the side wall of said nozzle, a reversiblepdirect current motor rotatable in a -direction determined by the polarity of the voltage applied thereto and having twoterminals for advancing and retracting said ller wire, a `source of direct voltage having two terminals, first switch means having first normally open and second normally closed contacts the states of which are concurrently changed, second switch means having first normallyopen Vand second normally closed contacts the states of which-are concurrently changed, means for connecting said first vcontacts and said second contacts of said-first switch means in series with one another across said source, means forconnecting said first contacts and said second contacts of said second switch means in series with one another across.

said source, means for connecting one terminal of said motor to the junction of said first and second contacts of said first switch means, means for connectingthe' other terminal'of said motor to the junction of said first` and second contacts of said second switch means, meansincluding said motor for driving the Vfiller wire through said aperture, and control means for selectively and alternatively actuating said first and second switch means for controlling the advancing and retracting of the filler wire.

27. An arc welding machine for supplying precisely controlled amounts of filler wire to a weld comprising means for establishing an arc between an electrode and a workpiece, feed means for feeding a ller wire toward and away from the arc, and means including timing means and said feed means for moving the wire toward the arc for a selectable period then away from the arc while the arc continues to control filler wire burn-off.

28. An arc Welding machine for supplying precisely controlled amounts of filler wire to a weld comprising means for establishing an arc between a nonconsumable electrode and a workpiece to puddle the workpiece, feed means for feeding a filler wire toward and away from the puddle in the workpiece, sensing means for detecting when the tip is in a preselected position, means including said feed means and said sensing means for moving the tip of the filler wire to said preselected position, and means including timing means and said feed means for moving the wire into the puddle for a selectable period followed by retraction of the wire out of the puddle while the arc continuesto -restrict ller wire 'burn-o.

29. An arc welding machine for supplying precisely controlled amounts of lllei wire to a weld comprising means for drawing an arc between a nonconsumahle electrode and a workpiece to puddle the workpiece, means comprising a reversible motor for -feeding a filler wire toward and away from the weld puddle, and means for energizing said motor for a selectable period to feed a predeterminable amount vof said ller wire into the weld puddle and thereafter energizing the motor in the reverse direction to retract the wire from the weld puddle to control ller wire burn-off while the arc continues.

30. An arc welding machine in accordance with claim 29 wherein said energizing means is deenergized upon retraction of said ller wire a predetermined amount with respect to the machine.

31. In an arc welding apparatus for welding a workpiece, a metallic nozzle engagea'ble with the workpiece, an electrode within said nozzle, working voltage means `for establishing a working direct voltage between said electrode and the workpiece, voltage supply means having two output terminals for producing a voltage which is high in magnitude relative to said working voltage, and means Ifor connecting one of said terminals to said electrode and manually actuatable means for alternatively connecting the other terminal of said voltage source means to said nozzle and to the workpiece.

32. In a filler wire driving mechanism for an arc welding apparatus having a nozzle, the combination of a support 4bracket attachable to the apparatus and disposable in preselected relation to the nozzle, a reversible driving motor supported by said support bracket, a tachometer generator supported by said support bracket and drivingly coupled to said motor for producing an output signal which varies in accordance with the speed of said motor, a driving roller and an idle roller 'both engageable with the wire for driving the wire, means for drivingly connecting said motor to said driving roller, control means responsive to the output voltage from said tachometer generator for controlling the speed ofgsaid motor, and means for sensing when the tip of said ller wire is in preselected positional relationship with the nozzle, said control means `further including means responsive to said sensing means for controlling the energization and deenergization of said motor for moving the tip of said ller the aperture in the nozzle, the combination of sensing means for sensing when the tip of the filler wire is in preselected positional relationship to said nozzle, and control means including said sensing means and said motor for moving the tip of said iiller wire into said preselected positional relationship with said nozzle.

34. The combination of claim 33 in which said sensing means includes means for sensing the electrical engagement of the tip of the iiller wire with the hollow nozzle.

35. The combination of claim 33 further including a wire-feed nozzle proximate the hollow nozzle and directed to direct ller wire passing therethrough to pass through the aperture in the hollow nozzle, and means for electrically insulating said wire Afrom said wire and nozzle when said wire is withdrawn therefrom, and in which said sensing means includes means for sensing the electrical engagement of the ller wire with said wire-feed nozzle.

: 36. The combination of claim 35 further including a support plate connected to said apparatus, and adjustable means supported by said support plate and supporting said wire-feed nozzle and adjustable to change the yangle of feed of the feed wire through the aperture in the hollow nozzle.

References Cited by the Examiner UNITED STATES PATENTS 788,539 5/ 1905 Klopf 20G-61.42 VX 2,235,385 3/1941 Rava 219-131 2,360,160 10/ 1944 Pickhaver 219-130 2,394,111 2/ 1946 Schaelchlin et al 318-293 2,460,990 2/ 1949 Kratz et al. v 219-131 2,516,037 7/ 1950 Williams 219-75 X 2,550,495 4/1951 Pilia 219-127 2,603,760 7/1952 Kocher 219-131 X` 2,731,536 1/1956 .Laur 219-130 X 2,752,469 6/ 1956 Price 219-'131 2,761,049 8/ 1956 McElrath et al. 219-130 2,766,361 10/1956 Landis et al. 219-131 2,791,673 5/1957v Arnaud 219-74 l2,892,925 6/ 1959 Butterfield 219-'-127 2,898,445 9/1959 Slezak 219-127 2,906,859 9/1959 Steele 219-130 2,922,871 1/1960 Hackman et al 219-131 2,935,674 5/1960 Hohne 3187-293 v'2,950,381 8/1960 Brennen et al 219-127l 2,957,977 10/ 1960 Sullivan 219-127 2,982,845 5/1961 Yenni et al. 219-75 X 2,993,984 7/ 1961 Sullivan 219-131 2,998,507 8/ 1961 Brenner et al. 2'19-127 ANTHONY BARTIS, Acting Primary Examiner.

RICHARD M. WOOD, JOSEPH V. TRUHE, Examiners. 

8. THE METHOD OF ACCURATELY CONTROLLING THE AMOUNT OF FILLER WIRE INTRODUCED INTO A WELD PUDDLE DURING AN ARC SPOT WELDING OPERATION WHICH COMPRISES THE STEPS OF ELECTRICALLY SENSING AN ARCUATE INITIAL POSITION OF THE TIP OF THE FILLER WIRE, ADVANCING THE FILLER WIRE INTO THE WELD PUDDLE AT A CONTROLLED RATE FOR A PRESELECTED PERIOD OF TIME, AND RETRACTING SAID FILLER WIRE AT THE END OF THAT TIME. 